The typical remedy for middle ear effusion is a myringotomy surgical procedure that involves surgically forming a slit in the eardrum to relieve a buildup or reduction of pressure in the middle ear cavity. A variety of ear ventilation tubes for insertion into such a slit have been introduced over the years. Such tubes attempt to maintain an opening for a sufficient period of time following surgery to allow pressure to equalize between the middle and the outer ears or to drain fluids from the middle ear.
Vent tubes have been developed with any number of shapes that promote, for example, ease of insertion or removal, resistance to clogging and one-way flow of fluids. However, although these tubes utilize any number of shapes and design variations, most of them maintain a uniform diameter center opening or lumen for conveying fluid from the middle ear into the ventilation tube.
It has been found that conventional vent tubes which have lumen diameters ranging from about 0.75 to 1.5 millimeters have a tendency to clog over time and to impede free flow of fluid when drainage is required. Because of the small size of the tympanic membrane and the risk of leaving a permanent perforation, there is a practical design limitation on the size of the lumen. A diameter found to be acceptable is about 1.27 millimeters.
A tube manufactured by Xomed, Inc., Product No. 10-20000, is known, which has a tube body with a conical shape and a lumen that increases in diameter in a direction away from the outer side of the eardrum. The Xomed tube is connected to the eardrum by means of a flange attached to the smaller diameter end of the tube body, the flange being located on the middle ear side of the eardrum for holding the tube in place. The Xomed tube is thus positioned in the eardrum with the small diameter end of the lumen exposed to the middle ear through the flange. While the Xomed tube appears to have the advantages of a cone-shaped lumen that expands on the outer ear side of the eardrum, it is believed that there are disadvantages in flow characteristics of the highly viscous middle ear fluids to having a narrow lumen opening facing the middle ear.